United States, European and Australian safety standards dictate that agricultural power take off shafts must be enclosed by an approved safety cover. Current Australian and United States standards allow for the safety cover to rotate with the shaft. However, the safety cover must stop rotating when it comes into contact with any object. This requirement is normally achieved by the use of a safety guard bearing between the safety guard and the power take off shaft.
Alternatively, the safety guard can be retained in a stationary position whilst the power take off shaft is operating. This is normally achieved by tying the safety guard to the tractor frame with a light duty chain.
European standards presently specify that the safety guard must not rotate with the power take off shaft. Thus, in Europe, the chained method described above is usually adopted.
Separate safety standards specify that tractors must be fitted with a metal power take off master guard. The metal master guard effectively covers the attaching end of the power take off shaft and a portion of the power take off shaft guard.
Power take off shafts typically incorporate a groove in the outer surface. Most current safety guards for use with power take offs have a safety guard bearing that has a flange or projection that rests in the groove in the power take off. For example, the safety guard bearing may comprise a split collar having a radially inwardly extending projection that resets in the groove on the power take off to thereby retain the split collar on the power take off.
In one presently commercially available power take off safety guard, the split collar includes three outwardly extending lugs. The safety guard includes a guard body having an open end that can be slipped over the yoke of the power take off. The guard extends away from the tractor to cover the power take off shaft.
In order to retain the guard on the power take off shaft, the guard body is provided with three openings that can receive the three lugs on the safety guard bearing. When the lugs from the safety guard bearing are inserted into the opening, the safety guard can be rotated so that the lugs move to a position in which it is not possible to remove the guard body from the lugs. In order to prevent the safety guard rotating back to a position at which the lugs can be removed from the body, a blocking member or stop member is inserted into place to stop relative rotation between the lugs and the guard body.
Other power take off safety guards currently available allow release of the safety guard by removal of snap ring, release of screw locks, compression of snap locks or removal of separate lock keys. All these methods for releasing the safety guard require the use of tools. It will be appreciated that such tools may not always be readily available.
A further disadvantage of known safety guards resides in those safety guards utilising separate locks that can become lost in the field.